sozymasti lujvo

x1 is September/the ninth month of year x2 in calendar x3.

Duration. For date, use masnso. Cf. pavmasti, nanca.

In notes:

pavmasti
x1 is January/the first month of year x2 in calendar x3.
xlima'i
x1 is September of year x2 in calendar x3.
sozmast
September.